1. Field of the Invention
The present invention relates to an arrival path direction estimation means in a radio communication device having an array antenna used in a digital radio communication system and a directional control means based on the arrival path direction estimation means.
2. Description of Prior Art
The signal a radio communication device receives is interfered with various signals and deteriorates receiving quality. An adaptive array antenna is known as an art that suppresses this interference and powerfully receives only the signal arriving from a desired direction. The adaptive array antenna can powerfully receive only the signal arriving from the desired direction by adjusting a weighting coefficient multiplying a receiving signal (hereinafter, this weighting coefficient is referred to as ‘weight’) and adjusting an amplitude and a phase applied to the receiving signal.
Further, the radio communication device requires a path timing detection circuit (hereinafter referred to as path search circuit) that detects a receiving timing of a desired signal at reception. The communication radio device can detect a more accurate receiving timing and estimate an arrival direction using a processing result at path search by combining this path search circuit with an adaptive array antenna art.
A conventional adaptive array antenna device having the path search circuit is disclosed in Japanese Unexamined Patent Application No. Hei 14 (2002)-84216. FIG. 1 is a block diagram showing the configuration of a receiver of a direct spread CDMA system having the conventional adaptive array antenna. The operation of the outline is described below with reference to FIG. 1. All signals of an array antenna 51 having multiple antenna elements 51-1 to N are input to a searcher 50 in FIG. 1. In the searcher 50, after mutual correlation operation processing with a known signal for every antenna is performed in a correlation processing unit 52, all the signals are input to an inter-antenna correlation estimation unit 54 installed in parallel to an antenna synthesis path timing detection unit 53. After the antenna synthesis path timing detection unit 53 converts a complex correlation value signal to electric power following the correlation processing of each antenna, high accurate path timing detection is implemented even in a low SNR (signal-to-noise ratio) by synthesizing both. Moreover, the inter-antenna correlation estimation unit 54 estimates an inter-antenna correlation value using the complex correlation value signal of each antenna after the correlation processing. The interface between an array antenna receiving signal processing unit 55 and the searcher 50 provides a signal that corresponds to the inter-antenna correlation value in addition to a path-timing signal. An adaptive array receiving unit sets an inter-antenna correlation estimate obtained from a searcher as an initial value of a weight update unit.
In the conventional receiver having the aforementioned configuration, however, a chip rate is speeded up in the direct spread CDMA system to implement a high-speed transmission rate. Consequently, since the time resolution of an arrival path increases and the electric power per path decreases, such a problem that the arrival direction estimation accuracy per path cannot be secured is caused. When a communication device does not presuppose high-speed travel, the accuracy increases if a correlation value is made average over multiple frames, but the follow-up of an array weight deteriorates. Moreover, for short packet transmission, such a problem that the correlation value cannot be made average over sufficient time intervals is also caused.
The present invention is made in consideration of such a point, and the first object is to estimate multiple path arrival directions and estimate the average arrival direction of the entire path after synthesizing the inter-antenna correlation value obtained for every path in a radio communication device having an array antenna.
Further, the second object of the present invention is to provide a radio communication device that can form a directional beam in the average arrival direction of multiple paths arriving with an angular spread even if the received power for every path is low.
Further, the third object of the present invention is to provide a radio communication device that secures communication of stable quality without deteriorating the follow-up of directional receiving.